Exothermic mixture for use on surfaces of molten metal in molds



Patented Sept. 2, 1947 EXOTHERMIC MIXTURE FOR USE ON SUR- FACES OF MOLTEN METAL IN MOLDS Marvin J. Udy, Niagara Falls, N. Y.

No Drawing. Application May 10, 1943, Serial No. 486,431

This invention relates to metallur y and has for an object the provision of an improved metallurgical method or process and the provision of an improved metallurgical product. More particularly, the invention contemplates the provision of an improved method or process for producing sound castings of metals such as iron and steel. The invention further contemplates the provision of products which may be employed in casting operations to inhibit or reduce pipingduring solidification of metal in casting molds and in ot molds.

When steel is poured into a mold, it forms almost immediately a thin skin of frozen metal against the cold surface of the sand or iron of the mold. The radiation of heat thereafter necessarily takes place through these surfaces, and, therefore, a casting usually will complete its solidification by the formation of thicker and thicker layers of solid metal around all the sides. The top portion, however, usually will remain molten longer than the rest because the hottest metal is usually at this point, having been the last to leave the ladle, and, also, because the heat is not conducted away by the air as fast as by-the walls of the mold. This is especially true where the casting is poured into an iron mold, for example, in the case of ingots. But it is evident that at some period a stage will be reached when all the outside of the ingot, or casting, will be covered by a skin of solid metal while the interior willstill be liquid. The liquid interior will continue to freeze and will, at the same time, contract, The result will be the shrinking of the molten'mass and, consequently, the formation of a cavity, known as a pipe, in the interior.

- The portion of the steel containing the pipe is of course defective and must be discarded at some time subsequent to casting. In the casting of ingots, the upper part, which contains the pipe, is cut off during the rolling or forging and goes back to the furnace to be remelted as scrap. vIn

the casting of steel castings, there is a large ad-' iunct to the castings situated above it, and so reg"- ilated in size and otherwise that it freezes after ;he casting itself, and thus contains a supply of nolten metal which is available to fill any cavity ghat forms in the casting. This adjunct is cut ifi" when the casting has cooled. In other words, :lle riser or feeder, as this extra part is called, aerves the same purpose for a steel casting as the ipper part of an ingot does for the ingot.

I have discovered that piping may be inhibited r reduced substantially by covering the surfaces f molten metal in ingot molds and in the risers 12 Claims. (ol. 22-141).

' and gates of casting molds with layers of slag of controlled fluidity at temperatures initially higher than the melting or freezing temperatures of the molten metals within the molds. The heat of the slag prevents solidification of the metals in the upper portions of the molds and thereafter the slag layers form insulating blankets which prevent rapid dissipation of the heat contained in the molten metal and thus cause the metal to be maintained in the molten state for longer periods of time. Supplies of molten metal for filling cavities formed in the casting, therefore, are maintained for longer periods of time and pipeforming tendencies are reduced. The sensible heat of the slags applied to the surfaces also aids in maintaining the metal in the molten state.

The use of a fluid slag is objectionable because it may tend to fiow with the molten metal into the cavity resulting from shrinkage and thus produce a defective casting. In practicing my invention,

I employ or produce slag of lower fluidity (or higher viscosity) than the molten metal of the casting to which it is applied, thus providing for preferential fiow of molten metal into the shrinkage cavity and avoiding the introduction Of slag into the cavity. The slag employed may be rel- 'atively viscous, plastic or even substantially solid.

In accordance with the invention, slag may be applied to or formed on a molten metal surface in any suitable manner or at any suitable temperature above the melting or freezing temperature of the metal. process of the invention, I employ slag at a temperature at or near, or even above, the castin or pouring temperature of the metal in order to' prevent any substantial transfer of heat from the metal to the slag initially. By employing slag at a temperature at or near the casting or pouring temperature of the metal, dissipation of heat from the molten'metal is greatly reduced. When the slag is employed at a temperature above the casting or pouring temperature of the metal, heat is transferred from the slag to the metal. When the molten metal is at a temperature lower than the casting or pouring temperature at the time of application of the slag, heat may be transferred from the slag to the metal even though the temperature of the slag is below the casting tempera- In a preferred method or I prefer to form slag layers by placing in contact with the molten'metal within casting molds exothermic reaction mixtures capable of igniting upon contact with the metal and capable upon ignition of reacting exothermically to produce slag products having suitable compositions and temperatures. Exothermic reaction mixtures of the invention preferably are of such compositions as to be capable of reacting upon ignition to produce slags having temperatures not substantially lower than the temperatures of the molten metals at the times of application of the slag thereto.

In carrying out a method or process of the invention, an exothermic reaction mixture of any suitable composition capable of reacting upon ignition to produce slag having a suitable composition and temperature may be employed. The preferred exothermic reaction mixtures of the invention are mixtures capable of reacting to produce iron oxide-bearing slags. Such reaction mixtures may comprise iron oxide, oxidizing material such as sodium nitrate or sodium chlorate, non-carbonaceous reducing material and heat-absorbin material. A reaction mixture may also comprise a small amount of finely divided carbon intimately mixed with the other components to aid in initiatin and propagating'the exothermic reaction. The reducing material preferably is present in the reaction mixture in amount suflicient to react with all of the oxidizing material and to reduce not more than a portion ofthe iron of the iron oxide, the components of the reaction mixture preferably are present in such quantities and are so proportioned as to be capable upon ignition of the reaction mixture of reacting exothermically to produce iron oxide-bearing slag and heat absorbing material preferably is present in amount suflicient to quickly thicken any fluid slag produced as the result of the reaction. Heat-absorbing material may be employed in amounts equal to about five to ten percent (5% to 10%) more or less, of the weight of the complete mixture. Fine...

ly divided carbon for aiding in initiating and propagating the reaction may be employed in any suitable small amount. Usually an amount equal to less than about one percent of the weight of the complete mixture produces satisfactory results Iron oxide may be employed as ferric oxide (FejzOs) or as magnetite (F6304) The iron oxide may be obtained from iron ore or from mill scale or from any other suitable source. Mill scale is a highly satisfactory source of iron oxide. The re ducing material may be silicon, magnesiumpr cal-- cium or a mixture or alloy containing two or more of these elements and which may contain one or more other elements. When aluminum is ,employed as the reducing agent, oxidizing material such as sodium nitrate may be omitted from the mixtures. Ferrosilicon may be employed advantageously and economically as reducing material. Any grade of ferrosilicon may be employed, but I prefer to employ ferrosilicon containing silicon in an amount in the range fifty to seventy-five percent by weight. Suitable heat-absorbing materials include carbon and quartz. Carbon in the form of crushed electrodes, charcoal or coke may be employed satisfactorily.

The componentsof the reactionmixtures of the invention, other than the heat-absorbing material, preferably are intimately mixed (as by grind ing together) in the form of particles small enough to pass a IOO-mesh screen. Heat-absorbing materials preferably are employed .in the form of particles as large as about one-halfinch or larger in size and not smaller than those capable of passing a 20-mesh screen; A mixture of particles in the range 4 to 20-mesh or 20-mesh to one-half inch produces satisfactory results. The reaction mixtures may be employed in the form of loose powders or in the form of agglomerates in which the particles are bonded together by means of the oxidizing material or by other suitable bonding means.

A reaction mixture of the invention, for all practical purposes, may be considered as consisting of two component parts, namely, (1) a heat-generating and slag-producing part comprising reducing material, oxidizing materia and slag-formin material and (2) a heat-absorbing part. The function of the heat-generating and slag-producin part is to generate a substantial amount of heat and develop a high temperature substantially instantaneously, and the function of the heat-absorbing part is to thicken liquid or fluid slag which may be formed as the result of the high temperature developed and thus form a relatively viscous slag which will retain the heat generated and remain in place as a porous insulating' covering for the metal.

When a reaction mixture of the invention is contacted with the surface of molten metal, such as iron or steel in a mold, the components of the heat-generating and slag-producing part react immediately to generate heat and produce a hightemperature slag. Because of the necessity of producing a high-temperature slag to insure maintenance of the upper surface portion of the metal in the molten state, the fluidity of the slag will be undesirably high initially. The heat-absorbing material commences to function substantially immediately after production of the slag to absorb heat and thus reduce the temperature and fluidity of the slag while permitting retention in the resulting slag layer of substantially all ofthe heat generated and thus providing a hightemperature high heat-containing insulating covering for the metal.

temperature be developed at the surface of the metal only substantially instantaneously. A substantially instantaneous high temperature will effectively prevent freezing of the surface of the metal and the relatively low-temperature slag the result that'a portion of the heat is absorbed and the slag is thickened. By employing relatively coarse heat-absorbin material, heat absorption is relatively slow, suflicient'heat bein absorbed to effect thickening of the slag without undesirable initial reduction of the temperature of the slag and without dissipationof the heat generated. .The use'of finely divided heatabsorbing material such "as quartz would result in an undesirable reduction of the temperature of the slag through too rapid absorption of heat and probably through endothermic reactions with the slag. Finely. divided carbon such as charcoal reacts, with the oxidizing material to generate heat, while coarse carbon is substantially non-reactive in the presence of the finely divided non-carbonaceous reducing agent and functions initially substantially entirely as a heat absorption agent. I

In the preferred exothermic reaction mixtures of the invention, I employ coarse carbon, such as coke, as the heat-absorbing material. After ig- In order for the reaction mixture to beeffective, it is necessary that a highsorbing material to form slag aaaaseo nition and thickening of such a reaction .mixture and during subsequent cooling and solidifl cation of the molten metal, the carbon oxidizes through contact with the air to generate additional heat and causes the production of porous slag both of which factors improve the insulation properties of the slag, causing the cooling period to be prolonged.

It is desirable, particularly for use in small ingot molds and in the gates and risers ofcasting molds, that the reaction mixture be applied to the metal immediately after pourin has been completed and that it be capable of reacting to develop a high temperature substantially instantaneously to prevent the formation of a skin of solid metal on the surface of the molten metal.

' 7 Reaction mixtures comprising sodium nitrate;

ferrosilicon, iron oxide and heat-absorbing ma- 3 terial such as coke or quartz and such mixtures which also contain small amounts of finely divided carbon may be employed with particular advantage. Such mixtures ignite substantially instantaneously when placed in contact with molten iron or steel; They react rapidly to generate large quantities of heat and produce hightemperature, fluid iron silicate slags which are thickened substantially immediately through the action of the heat-absorbing material. Such mixtures; when placed in contact with molten iron or steel, react toproduce slags having temperatures of about 2900 F.

In the production of large ingots, the heatgenerating and slag-producing part and the heat-absorbing part of the reaction mixture may be placed on the surface of the metal separately. Thus, for example, the heat-generating andslag-producing part may be placed in contact with the molten metal to produce a high-temperature fluid slag, and the slag may be thickened by the subsequent addition of heat-abof lower fluidity than the molten metal.

The following example illustrates exothermic reaction mixtures of the invention which have been employed effectively in carrying out the method or process of the invention, proportions of the components being shown in parts by weight: 1

Sodium nitrate (NaNOs) 25 Ferrosilicon (75% Si) 25 Mill scale 70 Coke 15 Charcoal 0.5

The above components were intimately mixed by grinding charcoal, sodium nitrate, ferrosilicon and mill scale together in a ball mill to form a mixture consisting of particles about ninety-five percent of which were small enough .to pass a 100-mesh screen, and the resulting mixture was uniformly mixed with coke consisting of particles small enough to pass a 4-mesh screen and too large to pass a. -mesh screen. The complete mixture was" applied to the surfaces of molten metals in the hot tops of ingot molds and in gates pipe. Comparative tests were conducted'employing similar molds, metals and casting temperatures but employing so-called pipe eliminator materials proposed heretofore for use in casting operations with the following results:

' Per cent of Prior Art Pipe Eliminator g gg to g Pipe 72. 74. 1a. to. p as.

A similar test omitting the use of any pipe eliminator material produced an ingot having a pipe extending-ithrough 77.1 Percent of the hot top.

In a complete the invention, an exothermic reaction mixture is contacted with the upper surface of molten metal in a riser or gate or hot top immediately ,after casting of the metal. The reaction mixture preferably is of such composition as to be capable upon ignition of reacting to produce slag having a temperature higher than the temperature of the molten-metal at the time of application of the slagthereto. The slag preferably is maintainedin contact with the metal until the metal has solidified.

The method or process and the products of the invention may be employed advantageously to reduce the depths of hot tops employed in ingot casting operations. Thus, the invention permits a substantial saving in operating costs by reducing the quantities of metal which must be removed from ingots and remelted as scrap. The invention also permits substantial savings in operating costs in the production of castings by providing for the maintenance of a sufllcient sup ply of molten metal in risers to insure the filling of cavities formed during cooling and solidification of the castings and thus duction of sound castings.

I claim:

1. An exothermic reaction mixture suitable for use in providing slag layers on the surfaces of molten metals in casting'molds and ingot molds to inhibit or reduce piping, comprising flnely divided iron oxide, sodium nitrate and non-carbonaceous reducing material and relatively coarse heat-absorbing material, the iron oxide, sodium nitrate and non-carbonaceous reducing material being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of reacting exothermically to produce molten slag and the heat-absorbing material being present in amount suiflcient to thicken the slag.

2. An exothermic reaction mixture suitable for use in providing slag layers onthe surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely divided. iron oxide, sodium nitrate and non-carbonaceous reducing material and relatively coarse carbon, the iron oxide, sodium nitrate and non-carbonaceous reducing material being presinsurlng the proentin such quantities and being so proportioned preferred method or process of thermically to produce molten oxide, sodium nitrate v 7 metals in casting molds and ingot molds to irr. hibit or reduce piping, comprising finely divided iron oxide, sodium nitrate and non-carbonaceous reducing material comprising silicon and rela tively coarse heat-absorbing material, the iron oxide, sodium nitrate and non-carbonaceous reducing material being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of reacting exoabsorbing material being present ficient to thicken the slag.

4. An exothermic reaction mixture for use in providing slag layers on the surfaces of molten metals in casting molds and ingot molds to in amount sufinhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate and non-car bonaceous reducing material and relatively coarse heat-absorbing material, the reducing material being present in the reaction mixture in amount suflicientto react with all of the sodium nitrate and to reduce a portion only of the'iron of the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of reacting e'xothermically to produce iron oxide-bearing slag and the heat-absorbing material being present in amount suflicient to thicken the slag.

5. An exothermic reaction providing slag layers on the surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate and non-carbonaceous reducing material and relatively coarse carbon, the reducing material being present in the reaction mixture in amount sufficient to react with mixture for use in slag and the heatall of the sodium nitrate and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be capable upon ignition of reacting exothermically to produce iron oxidebearing slag andthe carbon being present in amount sufiicient to thicken the slag..

6. An exothermic reaction mixture for use in providing slag layers on the surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely divided iron and non-carbonaceous reof the reaction mixture ducing material and relatively coarse coke, the

reducing material being present in the reaction mixture in amount sufilcient to react with all of the sodium nitrate and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantitles and being so proportioned as to be capable upon ignition of the reaction'mixture of reactin exothermically to produce iron oxide-bearing slag to produce iron oxide-bearing slag and the heatabsorbing material being present in amount sufficlent to thicken the slag.

8. An exothermic reaction mixture for use in providing slag layers on the surfaces of molten metals in casting molds and ingot molds to inhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate and non-carbonaceous reducing material comprising aluminum and relatively coarse heat-absorbing material, the reducing material being present in the reaction mixture in amount suillcient to react with all of the sodium nitrate and to reduce a portion only of the iron or the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of reacting exooxide, sodium nitrate and ferrosilicon and relatively coarse heat-absorbing material, silicon being present in sufllcient to react with all of the sodium nitrate and to reduce aportion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be capable upon ignition or the reaction mixture of reacting exothermically to produce iron oxide-bearing slagand the heatabsorbing material being present in amount sufficient to thicken the slag.

10. The method of producing sound metal castings which comprises pouring molten metal into 'a -suitable mold, contacting with an upper surface of molten metal within the mold an exothermic reaction mixture comprising finely divided iron oxide, sodium nitrate and non-carbonaceous reducing material and relatively coarse heat-absorbing material and thereby forming a layer of hot slag in contact with the molten metal, and.

maintainingthe metal and slag in contact until the metal has solidified, the reducing material being presentin the reaction mixture in amount sufllcient to react with all or the sodium nitrate and to reduce a portion only of the iron or the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be capable upon ignitlon'oi the reaction mixture of reacting exothermically to produce iron oxide-bearing slag and the heatabsorbing material being present in amount sufficient to inhibit or prevent the production of and the coke being present in amount suflicient to J inhibit or prevent the production of fluid slag.

'7. An exothermic reaction mixture for use in, providing slag layers on the surfaces of molten metals in casting molds and ingot molds toinhibit or reduce piping, comprising finely divided iron oxide, sodium nitrate and non-carbonaceous reducing material comprisingsilicon and relatively coarse heat-absorbing material, the reducing material being present in the reaction mixture in amount suiiicient to react with all of the sodium nitrate and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be'capable upon ignition of the reaction mixture of reacting exothermically 7 ca of molten metal within the mold an exothermic reaction mixture comprising finely divided iron oxide, sodiumnitrate and non-carbonaceous reducing material and relatively coarse carbon, and, I thereby forming a layer of hot slag in contact with the 'molten metal, and maintaining the metal and slag in contact until the metal has solidified, the reducing material being present in the reaction mixture in amount sufllcient to react with all of the sodium nitrate and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be ble upon ignition of the reaction mixture of use in" the reaction mixture in amount 9 reacting exothermically to produce molten iron oxide-bearing slag and the carbon being present in amount suflicient to inhibit or prevent the production of fluid slag.

12. The method of producing sound metal castings which comprises pouring molten metal into a suitable mold, contacting with an upper surface of molten metal Within the mold an exothermic reaction mixture comprising finely divided iron oxide, sodium nitrate and non-carbonaceous reducing material and relatively coarse coke and and slag incontact until the metal has solidified, the reducing material being present in the reaction mixture in amount sufiicient to react with all of the sodium nitrate and to reduce a portion only of the iron of the iron oxide, the components of the reaction mixture being present in such quantities and being so proportioned as to be capable upon ignition of the reaction mixture of reacting exothermically to produce iron oxidebearing slag and the coke being present in amount suflicient to thicken the slag.

MARVIN J. UDY.

REFERENCES CITED The following references are of record in the file of this patent: 

